1. Field of the Invention
The present invention relates to a method of forming a nitride semiconductor epitaxial layer suitably used for a nitride semiconductor device, and a method of manufacturing a nitride semiconductor device including such nitride semiconductor epitaxial layer.
2. Description of the Background Art
Various methods are being studied for obtaining a compact, high-performance nitride semiconductor device by separating a nitride semiconductor epitaxial layer formed on a substrate from the substrate.
For example, Japanese Patent Laying-Open No. 2003-037286 relates to a method of manufacturing a semiconductor device, and discloses, in order to reduce a stress applied by the substrate to a semiconductor layer and to facilitate separation of the semiconductor layer from the substrate, the steps of forming a first semiconductor layer on a mother substrate, irradiating a surface of the mother substrate opposite to the first semiconductor layer with light, to thereby form a thermal decomposition layer made of the first semiconductor layer having been thermally decomposed, between the first semiconductor layer and the mother substrate, forming a second semiconductor layer including an active layer on the first semiconductor layer with the thermal decomposition layer formed thereon, and removing the thermal decomposition layer, to thereby separate the mother substrate from the first semiconductor layer.
Japanese Patent Laying-Open No. 2007-221051 relates to a method of manufacturing a nitride-based semiconductor element, and discloses, in order to improve separation of the substrate from the semiconductor element layer to suppress reduction in yields, the steps of growing, on a first substrate, a semiconductor element layer having a layer made of at least one or more layers of nitride-based semiconductor, forming a second substrate on the semiconductor element layer, irradiating the second substrate with laser light that is transmitted through the second substrate and the semiconductor element layer and absorbed into the first substrate, to thereby separate the first substrate.
Japanese Patent Laying-Open No. 2003-178976 relates to a method of manufacturing a semiconductor device, and discloses, during manufacture of a semiconductor device having a layer at least containing a III-group element and N (nitrogen) on a Si-based substrate, forming a layer at least containing InN on a surface of the Si-based substrate at less than or equal to 700° C., and raising the temperature to more than or equal to 900° C., thereby forming a structure in which the surface of the III-group element Si-based substrate has a step shape formed by periodic recess-like stripes, recess portions serving as air gaps, in order to prevent cracks from occurring during epitaxial growth to improve distributions of a-axis orientation in a C plane.
Japanese Patent Laying-Open No. 2005-064188 relates to a method of recovering and reproducing a substrate as well as a method of manufacturing a semiconductor wafer, and discloses a method of recovering a first substrate including the steps of bonding a second substrate to a semiconductor layer epitaxially grown on the first substrate, and separating the semiconductor layer and the first substrate.